[windows] fix spawn [..]\mocha ENOENT error

[adammankowski1]

This applies to neutrino-preset-mocha
I couldn't run test command on the Windows, it was failing with

events.js:182
      throw er; // Unhandled 'error' event
      ^

Error: spawn <5 directories deep>\node_modules\mocha\bin\mocha ENOENT
    at exports._errnoException (util.js:1022:11)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:189:19)
    at onErrorNT (internal/child_process.js:366:16)
    at _combinedTickCallback (internal/process/next_tick.js:102:11)
    at process._tickCallback (internal/process/next_tick.js:161:9)
npm ERR! Test failed.  See above for more details.

No matter which version of node.js, or neutrino I have installed.

[eliperelman]

LGTM, thank you!